We deposited a number room temperature ionic liquids inside the channels of semi-packed columns and used these columns for gas chromatographic separation of mixtures containing a number of polar and non-polar compounds. We demonstrated that these columns can be used for rapid and highly efficient separation of the components of different mixtures. Moreover, the separation performance was greatly improved when an atomic layer deposited materials, such as alumina, were immobilized on the surface of silicon before the deposition of ionic liquids. Given the vast number of RTILs that could be employed for coating, these findings should broaden the applicability of the semi-packed GC columns invented in VT MEMS lab.